| Ti6Al4V titanium alloy with low density and high strength has excellent mechanical property,which is widely used in aerospace,navigation,bioengineering and etc.However,titanium alloy still can not satisfy the requirements of anit-wear and corrosion resistance under harsh conditions,which limits the further application of titanium alloy in the friction and corrosion fields to a certain extent.Therefore,it is necessary to further improve their friction and corrosion properties through surface coating technique.In this paper,titanium alloy was nitrided by the plasma nitriding process,and the Cr-DLC coating was prepared on the nitrided titanium alloy by the magnetron sputtering method,which has an important scientific significance for the improvement of tribological and corrosion properties on titanium alloy.The main research contents and conclusions are showed as follows:（1）The titanium alloy was nitrided by the plasma nitriding process,and the Cr-DLC coating was deposited on the surface of nitrided titanium alloy by the magnetron sputtering method,which solves the problem of mechanical property mismatch between titanium alloy and Cr-DLC coating The morphologies and chemical elements of Cr-DLC coating deposited on the nitrided titanium alloy were characterized,and the nano-structure,mechanical property,bonding force and bonding mechanism were analyzed.The results show that the surface of nitrided titanium alloy is composed of compound layer with the high N concentration and diffusion layer with the low N concentration,and the corresponding phases are composed ofδ-Ti N andα-Ti,respectively.The nano-hardness and elastic modulus of nitrided titanium alloy are 6.05and 143.13 GPa,respectively,which are increased by 69.94%and 19.01%compared with the titanium alloy,respectively.The amorphous C peak appears at the diffraction angle of～44°,and its structural characteristic is presented as the mixture of three types of structures,i.e.,the G peak at 1551 cm-1（graphite peak）,the diamond peak at 1390cm-1 and the D peak at 1350 cm-1（defect peak）,showing the amorphous state.The bonding force of Cr-DLC coating is 20.70 N,which is mainly attributed to the atomic diffusions among the Cr-DLC coating,Cr N interlayer and nitrided titanium alloy composite structure,and the bonding force between the Cr-DLC coating and the nitrided titanium alloy is improved.Moreover,the nanoindentation results show that the Cr-DLC coating has high mechanical property,and its nanohardness and elastic modulus are 19.29 and 168.8 GPa,respectively,which is mainly because the sp3-C diamond and sp2-C graphite structures in the Cr-DLC coating provide high hardness and high elastic modulus,respectively.（2）The tribological properties of titanium alloys,nitrided titanium alloys and Cr DLC coatings were investigated by the methods of reciprocating and rotary friction,and their wear mechanisms were also analyzed.The results show that under the condition of reciprocating friction,the average coefficients of friction（COFs）of titanium alloy,nitrided titanium alloy and Cr-DLC coating are 0.90,0.82,and 0.12 respectively,and the corresponding wear rates are 14.84,10.58,and 0.07 mm3·N-1·m-1,respectively,in which the average COF and wear rate of Cr-DLC coating are decreased by 86.67%and99.53%compared with the titanium alloy,respectively,showing the excellent antifriction and anti-wear properties.Similarly,under the condition of rotary friction,the average COFs of titanium alloy,nitrided titanium alloy and Cr-DLC coating are 0.48,0.42,and 0.11,respectively,and the corresponding wear rates are 2.96,2.52,and 0.09mm3·N-1·m-1,respectively,showing that the average COF and wear rate of Cr-DLC coating are also decresed by 77.08%and 97.00%compared with the titanium alloy,respectively.The averge COFs of Cr-DLC coating under the conditions of reciprocating friction and rotary friction are similar,but the wear rate of Cr-DLC coating under the condition of rotary friction is larger than that under the condition of reciprocating fricton,showing that the Cr-DLC coating presents better wear resistance under the condition of reciprocating friction,which is because the Cr-DLC coating under the conditions of reciprocating friction and rotary friction is subject to the alternating friction and rotary friction,respectively.The wear rate of Cr-DLC coating with the high elastic modulus under the condition of alternating friction is decreased by 33.89%compared that under the condition of rotary friction,which indicates that the Cr-DLC coating is more suitable for the working under the condition of reciprocating friction.（3）The electrochemical corrosion performances of titanium alloy,nitrided titanium alloy and Cr-DLC coating were evaluated by the open circuit potential（OCP）,potentiodynamic polarization curve（PPC）and electrochemical impedance spectroscopy（EIS）,and the electrochemical corrosion behaviours in 3.5%Na Cl solution were systematically analyzed with the corrosion model.The electrochemical test results show that the corrosion current density icorr of Cr-DLC coating is the smallest among the three kinds of samples,while the polarization resistance Rp is the largest,which indicates that the electrochemical corrosion resistance of Cr-DLC coating is better than those of titanium alloy and nitrided titanium alloy.The charge transfer resistance Rct of Cr-DLC coating is also larger than those of titanium alloy and nitrided titanium alloy,which indicates that the electron movement resistance in the Cr-DLC coating is larger than those in the titanium alloy and nitrided titanium alloy.Moreover,the Cr-DLC coating reduces the interface capacitance through complex ion diffusion channels,which is one of the main factors of electrochemical corrosion resistance. |
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